The invention pertains to physical vapor deposition target/backing plate assemblies, and to methods of forming physical vapor deposition target/backing plate assemblies. In particular applications, the invention pertains to methods of incorporating a bonding layer between a target and a backing plate in a physical vapor deposition target/backing assembly, with an exemplary bonding layer being a layer capable of forming a strong diffusion bond to the target at a temperature of less than or equal to about 500xc2x0 C. in a time of less than or equal to about 24 hours. A xe2x80x9cstrongxe2x80x9d diffusion bond is defined as a bond capable of passing a peel test described herein. In further applications, the invention pertains to methods of incorporating one or more of titanium, zirconium, and copper in a bonding layer between a target and a backing plate in a physical vapor deposition target/backing assembly.
Physical Vapor Deposition (PVD) targets have wide application in fabrication processes where thin films are desired, and include, for example, sputtering targets. An exemplary PVD process is a sputtering process, and an exemplary application of a PVD process is to form thin films across semiconductor substrates in semiconductor processing applications.
A prior art PVD process is diagrammatically illustrated in FIG. 1. More specifically, FIG. 1 illustrates an apparatus 10 comprising a PVD target/backing plate assembly 12 above a substrate 14. Assembly 12 comprises a sputtering target 16 joined to a backing plate 18. Target 16 can comprise any of numerous metallic elements and alloys, and backing plate 18 can comprise numerous electrically and thermally conductive materials, such as, for example, copper or aluminum.
Target 16 has a surface 20 from which material is ejected, and which can be referred to as a sputtering surface. In operation, surface 20 is exposed to ions or atoms which impact the surface and are utilized to eject material from the surface toward substrate 14. The ejected material is illustrated by arrows 22 in FIG. 1. Such ejected material lands on substrate 14 to form a thin film (not shown) over the substrate.
Backing plate 18 provides several functions during the sputtering application illustrated in FIG. 1. For instance, backing plate 18 is typically provided with a shape configured to enable assembly 12 to be removably retained within a sputtering apparatus chamber (not shown). Also, backing plate 18 is typically formed of an electrically/thermally conductive material and is utilized for passing an electric field to sputtering target 16. An interface between target 16 and backing plate 18 should preferably comprise a bond strong enough to retain target 16 to backing plate 18 during a sputtering operation, and yet also comprise a continuous, uniform and electrically conductive construction so that an electric field can be passed uniformly across the interface from backing plate 18 to target 16. Among the methodologies presently utilized for forming a target-to-backing plate interface is a methodology of providing solder (shown as 15 in FIG. 1) between a target and backing plate to bond the target to the backing plate. The solder can comprise, for example, one or both of tin and indium.
A difficulty in utilizing solders is that the solders frequently do not adhere well to a target material, and accordingly a target can separate from a backing plate if only solder is utilized in the backing plate/target bond. Such problem can be particularly pronounced with targets comprising one or more of tantalum, cobalt, zirconium, platinum, iron, niobium, molybdenum, chromium, aluminum, copper and manganese. In order to overcome such difficulty, a transition layer 19 is frequently provided over a target surface prior to bonding the target surface to a backing plate. In the shown target/backing plate construction, target 16 has a surface 17 which is ultimately to be utilized in forming a bond with backing plate 18. Transition layer 19 is formed over surface 17 prior to bonding the target with the backing plate.
Transition layer 19 typically comprises nickel. The nickel is considered to adhere better to various target materials than does an indium or tin-based solder, and in turn an indium or tin-based solder is considered to adhere better to the nickel than to the target material. Accordingly, the nickel layer 19 can be ultimately bonded with solder 15 to retain the target 16 to backing plate 18
Nickel-containing transition layers improve adhesion of various target materials to backing plates. However, it is found that even when such layers are provided, problems can still be encountered with separation or delamination of a PVD target from a target/backing plate assembly during a sputtering process. Nickel-containing transition layers can be particularly unsatisfactory when utilized with target compositions comprising one or more of Ta, Co, Zr, Pt, Fe, Nb, Mn, Cr, Al, Cu. The separation of a target and backing plate can occur, for example, at an interface between the nickel transition layer and the target. If delamination exceeds more than about 5% of the area of a target surface, the target/backing plate assembly can be rendered inoperable in that it will not perform within desired parameters. In some instances, a delamination of greater than or equal to about 1% can render a target/backing plate assembly inoperable. It would, accordingly, be desirable to develop new methodologies for adhering targets to backing plates to avoid the delamination problems associated with nickel transition layers.
In one aspect, the invention comprises a PVD target/backing plate assembly. The assembly includes a PVD target having a surface, and a bonding layer on the surface. The bonding layer has a different composition than the target surface, and a backing plate is provided to be separated from the PVD target surface by at least the bonding layer. The bonding layer can comprise a material capable of forming a strong diffusion bond to the target in less than or equal to about 24 hours at a temperature of less than or equal to about 500xc2x0 C., and can comprise, for example, one or more of copper, titanium and zirconium. In particular embodiments, the bonding layer can consist of, or consist essentially of, one or more of copper, titanium and zirconium. A xe2x80x9cstrongxe2x80x9d diffusion bond is defined as a bond capable of passing a peel test described herein.
In another aspect, the invention includes a method of forming a PVD target/backing plate assembly. A bonding layer is formed on a surface of a PVD target, and a backing plate is joined to the bonding layer. Accordingly, the backing plate is separated from the PVD target surface by at least the bonding layer. The bonding layer can comprise, for example, one or more of copper, titanium and zirconium.